Production process for a moulded multilyer lining

ABSTRACT

Production method for a multilayer lining for thermal and sound insulation with the steps of blending reinforcement fibers and polyamide matrix material, in the form of fibers, flakes or powder, and forming a web of said blend; layering said blended web and at least an additional layer chosen from an open cell foam layer, a heat reflective layer, or another of said blended web inside a mold; treating the stacked multilayer material with pressurized saturated steam, such that the polyamide matrix material in the blended web is melting at a temperature under steam pressure that is lower than the melting temperature of the polyamide matrix according to DSC, thereby binding the reinforcement fibers together thus consolidating the blended web forming a porous reinforcement layer, and all layers of the multilayer are laminated together.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a U.S. National Phase Application of International ApplicationNo. PCT/EP2012/054383, filed Mar. 12, 2012, which claims the benefit ofpriority to European Patent Application No. 11159402.4, filed Mar. 23,2011, which is incorporated herein by reference.

TECHNICAL FIELD

The invention relates to a method of producing a moulded multilayerlining for heat and sound insulation, for in particularly the enginecompartment of motor vehicles.

BACKGROUND ART

Acoustical and thermal liners for application to vehicles are well knownin the art. These liners typically rely upon both sound absorption, i.e.the ability to absorb incident sound waves, and transmission loss, i.e.the ability to reflect incident sound waves, in order to provide soundattenuation. They also rely on thermal shielding properties to preventor reduce the transmission of heat from various heat sources (engine,transmission and exhaust system), to the passenger compartment of thevehicle. Such liners are in particularly used in the engine bay area ofa vehicle, for instance employed as an engine cover so as to attenuatethe sound of the engine closer to its source.

In the engine compartment of motor vehicles, including passenger andcommercial vehicles, sound proofing parts in the form of absorbers areincreasingly being used to reduce engine noise. In general, theseabsorbers are designed as moulded articles to reduce the exterior andinterior noise of vehicles. The moulded articles may be made from webs(e.g. cotton) or from polyurethane foam, and typically have thermostabilities up to about 160° C.

In certain areas, such as exhaust manifolds, hot air recirculation areasor around the engine itself, the moulded articles may be subjected tohigh thermal loads. Thus these moulded articles are often laminated,partially or completely, with aluminium foil to serve as heat reflectorsin order to protect the underlying nonwoven. In general the aluminiumfoil is thick enough to function as the carrier layer, enabling themechanical properties for the part to be self-supportive. The soundabsorbing material is kept as loose material and as thick as possible tooptimise the acoustic properties of the part. For example DE 8700919discloses such an aluminium laminate with foam glued to the inside forinsulating purposes. Other examples are made of sandwiching loosefibrous material mats between two metal foil layers whereby the metallayers do have structural carrier properties.

In recent times composite thermal liners are partly replacing thetypical heat shield trim parts. These composite liners are generallyformed as multilayer assemblies. These assemblies are build with athermally exposed layer having reflective and impervious functions, anda composite layer having good thermal insulating, mechanical andstructural properties and sometimes with an additional top layer forappearance and imperviousness properties. These types of liners areproduced using injection moulding or compression moulding. Thedisadvantage of these composite thermal liners is that they areimpervious and heavy structural parts. Although they have good thermaland structural properties, they lack acoustic and thermal attenuatingproperties in most of the cases.

While a number of adhesives, adhesive webs and binding fibers have beenspecifically developed over the years to secure the various layers ofthe laminates together, laminated liners and insulators have an inherentrisk of delamination and failure. This potential risk is significantmainly due to the harsh operating environment to which such liners andinsulators are subjected. Many liners and insulators are located nearand/or designed to shield hot heat sources such as the engine,transmission and components of the exhaust system. As a result theliners and insulators are often subjected to temperature in excess of180° C., at which the adhesives or binders show a strong and fastdegradation over time.

In addition parts directly mounted adjacent to the engine are likely tovibrate and cause noises due to vibrations transmitted from the engine.These vibrating parts can form an unwanted additional noise. Anotheraspect is the fatigue properties of the lining involved, the frequencyof the vibration can have a negative effect on the overall lifespan ofthe lining.

A further disadvantage of the state of the art is the high temperatureneeded to obtain the final composite. The heating temperature to beachieved is dependent on the matrix polymer. In general to form thecomposite, the matrix and reinforcement fibres are heated using dryheating methods like hot air, contact heating or infrared heating. Inorder to compensate for the temperature loss for instance from theheating device to the moulding device, the product is normally heatedabove the true melting point of the matrix polymer or above theactivating temperature of the binding resin. Heating of a polymer abovethe melting point accelerates degradation.

Using a contact heater has the additional disadvantage that the producthas to be compressed to obtain a good transfer of heat throughout thethickness of the product. Hot air is generally used at a temperatureabove the melting temperature of the binder polymer so the polymer getsheat damaged, while the use of infrared heating is only feasible forthin materials. In thicker materials the amount of energy needed to heatthe inner material is damaging for the outer surface polymers. Thismethod is normally used only for a thickness up till 4-5 mm.

Using contact heaters in a multilayer lining including an open cell slabfoam layer will cause a collapse of the foam in particularly in the skinof the slab foam making it impervious to air borne sound waves, therebydeteriorating the overall acoustic absorption of the part.

Another disadvantage is the fact that most thermoplastic polymers usedas matrix fibres and as reinforcement fibres have their meltingtemperature close to each other for instance the melting temperature asmeasured using Differential scanning calorimetry (DSC) according toISO11357-3 of poly ethylene terephthalate (PET) is in the range of230-260° C., of polypropylene between 140-170° C., of Polyamide-6(PA6.6) between 170-225° C. and of Polyamide-6.6 between 220-260° C.Using matrix fibres and reinforcement fibres both being thermoplasticpolymers, for instance PA6.6 as matrix and PET as reinforcement, havingto heat them above the melting temperature of the matrix fibres willalso cause the reinforcement fibres to start melting or softening. Thiswill lead to a collapse of the structure, forming a very compactcomposite.

Felts are widely used particularly in automotive industry for theirthermal and acoustic insulation properties. The trend is towardsrecyclable materials; therefore thermoplastic binders have taken asignificant share in the last years. Fibers made of high performancepolymers such as polyesters, polyamide are highly interesting due totheir mechanical and heat resistance properties. But the necessarybinding agent form the limitation to their utilization in moulded 3Dparts.

The binding agents used so far always have a lower melting point thanthe reinforcement fibres, rendering in relatively weak performancebehaviour to the moulded fibre web and limiting its utilization totempered areas in the vehicle. None of these types of moulded fibre websis suitable for the high temperature exposure of the engine bay orcompartment, particularly of the engine contact areas. Some of thesebinders are modified polymers (Co Polyester (CO-PET) as an example)having pour behaviours due to their modified structure beingparticularly sensitive to hydrolysis phenomena.

The processes for moulding such felts as known in the state of the artare a ‘cold” moulding process where the felt is pre-heated by variousmeans, and then transferred to a cold mould in which it is compressed inorder to obtain the part shape or a ‘hot” moulding processes, where thefelt is introduced in a closed mould, in which a heat transfer media,like air, is introduced for bringing the binding agent to its meltingpoint, and then released. The part is then cooled down, inside the toolor outside, with or without cooling assistance. (See for instance EP1656243 A, EP 1414440 A, and EP 590112 A) Only after complete coolingdown to a temperature at which the material is set, the part can betaken out of the mould and transported.

Fibrous composites as disclosed are generally used in combination withadditional layers, like the reflective layers as discussed or with foam.Foam can be applied to such fibrous composites by direct back foaming(injection foaming or foam moulding) the foam. However often the foam isfirst produced as slab foam and cut into the thickness desired. For thelamination of the foam to adjacent fibrous layer generally hotcompression moulding is used. The stack of layers is put between two hotplates to melt the material and obtain a lamination of the layers.Compression is needed to help the transfer of heat to the porousreinforcement of the layered material. A disadvantage of such a method,in particularly where foam layers are used, is that the foam collapsesand forms a skin layer on the open cell structure. This skin layerdeteriorates the overall acoustic absorbing performance of the open cellfoam.

SUMMARY OF INVENTION

Thus it is the object of the invention to provide a process forproducing a moulded multilayer lining, for in particularly the enginecompartment of motor vehicles, having comparable heat insulating andsound proofing properties, but which are lighter and maintain therestructure over long time exposure to the thermal load in the area ofuse.

The object is achieved by the production process for a steam mouldedmultilayer lining according to claim 1.

In particularly by using the production method according to theinvention comprising at least the steps of

-   -   blending of reinforcement fibers and polyamide matrix material        in the form of fibers, flakes or powder, and forming a web of        said blend;    -   layering a first of said blended web and at least an additional        layer chosen from an open cell foam layer, a heat reflective        layer, or a second of said blended web inside a mould;    -   treating the stacked multilayer material with pressurized        saturated steam, such that the polyamide matrix material in the        blended web is melting at a temperature under steam pressure        that is lower than the melting temperature of the polyamide        matrix according to DSC, thereby binding the reinforcement        fibers together thus consolidating the blended web forming a        porous reinforcement layer, and all layers of the multilayer are        laminated together.

It was found that using a direct steam moulding process on polyamide asa binding material, the softening and melting point of polyamide isshifted to a lower temperature under steam pressure as the normalmelting temperature of polyamide measured according to DSC. By usingthis knowledge it is now possible to make parts that in use have ahigher melting temperature and are able to be heat stable at much highertemperatures than the state of the art materials. In addition it wasfound that the polyamide material used in the reinforcement layer isenough to also laminate adjacent layers. Surprisingly, layers like foamor heat reflective layer, without the need of additional matching gluelayers. In particularly it was found that using direct steam moulding onadditional foam layers did not have any negative effect, for instancemelting of the foam, on the acoustic properties of the foam layer.Therefore maintaining the advantageous acoustic properties of skinlessopen cell foam as produced.

The production process according to the invention can be used directlyto steam mould the multilayer lining in a 3 dimensional shape, like anengine bay covering panel, a top-, side- or undercover for an engine, anoil pan cover, an under engine shield, a fire wall, and at leastpartially covering outer dash panel, an air guiding panel behind thecooler of the engine bay, a parcel shelf or a trunk load floor, to serveas an automotive trim part in the interior of the car.

In the following the steam moulded multilayer lining according to theinventive process and the steam moulding process will be explained inmore detail and with examples of the use of such material.

Production Process

In the method according to the invention, high modulus reinforcingfibres are blended with matrix forming material in the form of polyamidefibres, flakes or powder to form a web by any suitable method such asair lay, wet lay, carding etc. This web is then heated using saturatedsteam to melt the polyamide matrix material at a temperature that islower than the melting temperature of the polymer as measured usingDifferential scanning calorimetry (DSC) according to ISO11357-3. Forexample the melting temperature T_(m) of polyamide-6 (PA-6) is 220° C.as measured using DSC. However the melting temperature of the same PA-6under steam pressure according to the invention is for example 190° C.

The web is placed in a pressure-resistant mould with at least one steampermeable surfaces. The mould is closed and clamped to withstand theinternal pressure. Saturated steam of at least 9 bars absolute pressureis applied to melt the binder. Saturated steam above 20 bars absolutepressure is not economical anymore. Preferably a range of 11 to 15 barsabsolute pressure is a good working range. The actual shift of themelting temperature of the polyamide is dependent on the steam pressuregenerated in the cavity the product is steam moulded in. The choice ofthe pressure used is therefore also dependent on the melting temperatureof the reinforcement fibres. For instance using PA-6 as binder fibresthe preferred pressures are 11 to 15 bars absolute pressure.

By using steam instead of the usual hot air, hot plates or IR wave it ispossible to shift the melting point of Polyamide to a lower temperatureusing the effect of the water molecules in the steam. The effect ofwater on polyamide is known and is normally considered a disadvantage;many prior art describes ways to avoid the effect or try to prevent it.Unexpectedly it is just this effect, which makes it possible to combinepolyamide material applied in the form of powder, flakes or fibres withother thermoplastic fibres with similar melting points as measured withDSC, like polyester (PET), using polyamide as the sole binding material,keeping the reinforcement fibres, like PET, in its fibrous form. It isnow possible to obtain a heat stable moulded product with a porousstructure thereby enhancing the acoustic properties, like absorption andairflow resistivity, as well as the thermal conductivity.

The effect of steam is based on a reversible diffusion mechanism. UsingPolyamide, in form of small fibre diameter or fine particles, themelting and solidifying is fast and provides short production cycles.Once the steam is released from the mould the Polyamide transforms intothe solid state and the part can be demoulded as a stiff part. This isan advantage compared to other thermoplastic binders that need to beexplicitly cooled inside or outside the mould before obtaining astructural part which is to be handled.

Because the overall temperature used, can now be kept much lower incomparison with the heating methods without steam, the resilience of thePET fibres is staying intact, leading to a more lofty material.Furthermore it was found that the binding of the PA was enough to obtainthe required stiffness of the final product. Because the PET fibres keeptheir resilience and the PA molten matrix material only binds thecrossing points. The material keeps its lofty appearance due to the voidvolume in the web. Therefore the final product will still be airpermeable. Furthermore it was found that also using glass fibres as thereinforcement fibres together with polyamide as the matrix the use ofsteam is advantageous. Due to the precise regulation of the bindingproperties less energy is needed for the process, both during heatingand during cooling.

In the heating process according to the state of the art the material isheated up to the melting point of the thermoplastic matrix material. Thecooling down of the material is slow due to the slower convection of theheat out of the product and because the material collapsed, due to lackof resilience of the reinforcement fibres and has become compacter. Sothe molten condition will continue for a longer period. As a result itis more difficult to regulate the amount of binding. Furthermore duringthis cooling period the material stays soft because of the longer meltedstate of the binding matrix and is therefore more difficult to handle.This is in particularly the case for larger automotive trim parts, likeheadliner or load floor for a truck or larger vehicle.

Unexpectedly, it was found, that using the material and the processaccording to the invention, as soon as the steam was taken away from thematerial the process of melting immediately stopped and the materialobtained is at solid state again. This is an advantage in the ability toreduce production cycle times due to immediately hand able material. Thefact that the melting process can be stopped immediately is also a veryprecise way of regulating the binding properties and therefore theporosity of the material. Which is important for the air permeabilityproperties of the material.

The use of polyamide in a discrete form like flakes, powder or fibers,is necessary to guarantee a discrete binding of the reinforcementfibers, to obtain a porous but consolidated structure. Due to thediscrete but full consolidation of the reinforcement fibers a highbending stiffness as well as dynamic stiffness can be obtained. As thematerial chosen preferably are thermo stable above at least 180° C., amaterial is obtained that maintains its structure, in particularly willnot soften or sack upon long time exposure to a high thermal load. Asthe consolidation of the polyamide and the reinforcement fibers is onlybased on the softening and melting of the polyamide under influence ofthe direct treatment with saturated steam under pressure, it is notnecessary to compress the reinforcement layer more than necessary toobtain the wanted 3 D shape of the final product.

Surprisingly it was found that laminating of additional layers to theporous reinforcement layer is possible in the same steam mouldingprocess step. It was even found that the PA matrix material was strongenough to be used as laminating binder to bind additional layers forexample in a combination with an open cell foam layer and/or areflective layer such as aluminium foil and/or a scrim layer.

Even more surprisingly it was found that using the steam moulding in thetemperature range according to the invention the foam material was notchanged in acoustic performance. In the normal hot moulding methodsaccording to the state of the art the foam is normally heated to atemperature at which the foam softens and forms a skin at the outerlayer or even worst shrinks in volume or collapses. This has adeteriorating effect on the quality of the foam after the moulding aswell as on the acoustic performance. An unwanted shift can be seen inthe sound absorption after moulding, while comparing to the originalstate. At worst the shift can be transformed in a lost of soundabsorption overall.

Steam is known to regenerate the foam back to its original componentsand therefore normally not used for moulding of parts where adegeneration of the material is unwanted. Surprisingly the processaccording to the invention does not show any measurable impact on thestructural and acoustic properties of the foam treated. As the foam isin particularly not melting during the steam process the originallyobtained open cell structure during the foam production is maintained.The binding of the porous reinforcement layer with the foam layer issolely coming from the molten droplets of polyamide binder material.This is enough to obtain a stable laminate binding. This has theadditional advantage that in thermally loaded environments like theengine bay the temperature for delamination is much higher than with thematerial normally used. In addition the thermally weak link is no longerthe binder itself.

It was even found that reflective material could be laminated directlywith the porous reinforcement layer according to the same principle.However in the case of metal foils, in particularly aluminium foils thelamination surface in contact with the porous reinforcement layer mightbe pre-treated to enhance the lamination.

If necessary an additional polyamide binder layer, in the form of afilm, powder, flakes or a scrim layer can be put in-between the layersto enhance the binding properties.

The Porous Reinforcement Layer

The porous reinforcement layer is an air permeable composite withincreased stiffness of randomly disposed binding material andreinforcement fibers held together at fibre crossover locations byessentially discrete droplets of the thermoplastic binding material.

The material used as thermoplastic binding material is a polyamidematrix in the form of powder, flakes or fibres. The use of polyamidefibres in the porous reinforcement layer is the most preferred, asfibres generally blend together better and stay that way during thehandling of the web before consolidation. In particularly flakes orpowder can fall between the reinforcement fibres out of the web byhandling without consolidation.

As polyamide all types of mixtures of polyamide are feasible, preferablyat least one of COPA (Co-polyamide), Polyamide-6 (PA-6) or Polyamide-6.6(PA6.6). It is expected that normal used additives in the basicpolyamide recipe are part of the basic polyamide material as claimed,for example chemical compounds to obtain Ultra Violet Resistance oradditional chemicals for increasing heat stability.

The use of polyamide binding fibers is most preferred and used in theexamples and preferred embodiments however the use of powder or flakescan be used as well in the same examples with comparable results.

The reinforcement fibers can be

-   -   mineral based fibers, like glass fibers, basalt fibres or carbon        fibers, and/or    -   man-made fibers having a melting temperature measured according        to DSC, which is higher than the melting temperature of the        polyamide under steam pressure, like polyester fibers, and/or    -   natural fibers, like flax, coconut or kenaff fibers.

In particularly the reinforcement fibres can be any thermoplasticpolymer based material with a melting temperature according to the DSCmeasurement, which is higher than the melting temperature of thepolyamide binder material in a steam environment. For instance man madefibers like PET (polyester terephthalate) with a melting temperature ofbetween 230-260° C. can be used as reinforcement fibre. The choice ofmaterial is based on the overall heat stability requirements of thefinal product and on the price of the individual materials.

Also mixtures of man made fibers with mineral fibers can be used asreinforcement fibres, for instance PET together with glass fibers (GF).Using such combinations will increase the loftiness of the final layerand can be defined as an acoustic reinforcement layer, see separatedescription of this layer for more details. The reinforcement fibres canbe cut fibres, endless filaments or roving dependent on the materialproperties needed.

The starting material for the reinforcement layer is a mat of randomlydisposed binding material and reinforcement fibres, that can be madeaccording to methods known in the art, for instance using air laid, orcarding technology or by direct forming after extrusion of the fibrematerials. The produced mat can be pre consolidated to enable easierhandling for instance by needling.

The ratio of polyamide binding material to reinforcement fibres is suchthat after the steam treatment the material stays porous. Preferablybetween 20 and 60% by weight of polyamide binding material.

Acoustic Reinforcement Layer

The acoustic reinforcement layer is a lofty version of the reinforcementlayer with increased sound absorbing properties.

The binder material is the same as disclosed for the porousreinforcement layer, however the reinforcement fibres can be anycombination or blend of mineral based fibers, like glass fibers, basaltfibres or carbon fibers, and man made fibers having a meltingtemperature measured according to DSC, which is higher than the meltingtemperature of the polyamide under steam pressure, like polyesterfibers, an/or natural fibers, like flax, coconut or kenaff fibers. Forexample a combination of PET (polyester terephthalate) with a meltingtemperature of between 230-260° C. together with glass fibers would workwell as reinforcement fibres.

It was found that by using such a combination of fibres the materialmaintains its loftiness during the steam moulding process. The materialdoes not only have an increased stiffness, but also an increasedacoustic absorption.

Mineral fibers like glass fibers are fine fibers and as such preferredfor acoustic absorption, however upon heat treatment they tend to loosetheir volume, and therefore the original sound absorptive properties.Surprisingly, it was found that man made fibers or natural fibers chosenproperly, such as polyester fibres or kenaf fibers, maintain theirrigidness during the steam moulding of the lining material. Thereforethe volume of the material is maintained and the consolidated materialstays porous, hence the original acoustic absorbing properties are stillgiven.

Preferably a mixture of approximately 20-40% by weight of polyamide,approximately 20-50% by weight of Glass fibers and 20-50% by weight ofPolyester fibers or natural fibers, would work well.

The reinforcement fibres can be cut fibres, endless filaments or rovingdependent on the material properties needed.

Heat Reflective Layer

Together with the fibrous porous reinforcement layer at least a heatreflective layer can be used. The surface facing the heat source,generally the engine or parts of the power train or exhaust line or thesurface exposed to sunlight, may be covered, either partially orcompletely, with a heat reflective covering layer at least in the areaof increased thermal load. The reflective covering layer should be heatstable and able to reflect infrared radiation either from the heatsource or the sun, to obtain a good heat insulation of the trim part,preferably the reflective covering layer is one of a metal foil layer,preferably stainless steel or aluminium foil layer, or an aluminisedtextile or nonwoven, or a textile made of aluminium fibres. The heatreflective layer should at least be able to resist steam treatmentwithout deterioration.

The reflective covering layer is preferably between 20 and 150 μm, morepreferably between 50 and 80 äm. The low thickness can be used since thereinforcement layer is performing the main static function, thereflective layer its only function is in principle reflecting heatradiation.

Although not necessary in all cases the reflective covering layer can beat least partially micro perforated. The micro perforating can be doneby known technologies like needling, slitting, micro fissuring or punchtechnologies. By means of an optional perforation of the reflectivelayer, the heat reflecting effect of the layer is maintained, howeverthe transmittance for acoustic waves is achieved in this area so thatthe aluminium foil-cladded side of the multilayer lining facing thesource of sound maintains the acoustic activity thereof.

Particularly in the case the reflective covering layer material ofchoice is non porous or non perforated, the heat entrance preferablyshould be at the side of the fibrous trim part that is not covered withthe reflective covering layer to optimise the steam penetration into theporous reinforcement layer.

In case of the use of reflective covering layers at both sides of thematerial, at least one of the layers used should be perforated and/orporous enough to enable a steam flow in the fibrous layer.

Also a reflective material layer can be used in between tworeinforcement layers according to the invention. This layer preferablyis perforated or porous, however the foil being perforated or porous isnot necessary, if the steam flow is entering the mould from both mouldhalves instead of via only one mould halve.

Foam Layer

As an additional layer an open cell foam layer can be used. The foam ispreferably skinless foam. Slab foam, produced continuously ordiscontinuously, is most preferred, as this foam is cut into sheetsafter foaming and curing, therefore the open cell structure is directlyaccessible without any skin.

Preferably the foam layer is at least short-term thermo stable between160 and 220° C., for instance it is made of open cell polyurethane (PUR)foam, or a polyester (PET) foam.

Polyurethane foams are made by addition reaction of polyisocyanates andpolyols. Additives are used as needed. Examples of PUR foams that can beused in the lining according to the invention are for instance disclosedin EP 0937114 or EP 937109 A.

In particularly for the use in the engine bay area or in areas with anincrease thermal load the use of a flame retardant for instancetreatment with a liquid and/or solid retardant and or incorporating sucha retardant in the foam is favoured. The use of foam with additionalgraphite for instance as disclosed in EP 1153067 or U.S. Pat. No.6,552,098 would be preferred.

The full disclosure of these documents in particularly regarding theproduction process and the material composition of the slab foam areincorporated herein by reference.

Industrial available foams, prepared as slab foams, that can be usedwith the lining according to the invention are for instance ACOUSTIFLEXS15 (semi-rigid), or ACOUSTIFLEX F 25 (flexible) from Huntsmann, orFlexidur 15 FR+ (semi-rigid) or Rigidur 10 (semi-rigid) by Foampartneror the range of Thermoflex semi-rigid foams in different grades anddensities made by Eurofoam like for instance Thermoflex 15, Thermoflex15 MDA, Thermoflex 15 MDA VW, Thermoflex 16, Thermoflex 22 and theflexible Thermoflex foams like T-flex 16 or T-flex 22.

Preferably the density of the foam is between 8 and 40 kg/m, morepreferably between 12 and 30 kg/m³. As the open cell foam will add tothe overall noise attenuation of the lining according to the invention,the air flow resistance is preferable in the range of 100 to 5000(Ns·m³) for a thickness of between approximately 6 and 45 (mm) for theslab foam before moulding.

Surprisingly it was found that the foam layer does not change itsacoustic properties during the steam treatment, in particularly the timeand conditions are such that the foam is keeping the open cell foamstructure. In particularly, the closure of the skin layer, as can beseen with foam laminated in a standard hot moulding tool, could not beobserved with the method according to the invention. Therefore theacoustic properties of the open cell foam are fully maintained in thelining according to the invention.

If the lining is used for a structural part with a high mechanical loadthe foam layer used can be chosen to enhance the overall structuralproperties, for instance by choosing a more rigid foam layer, forinstance made of polyurethane or polyester, or by adding reinforcementfibers to the foam layer.

Additional Layers

Preferably additional layers can be used. For instance an aestheticcover, or an anti sticking layer, to prevent the laminated lining fromsticking to the walls of the moulds can be needed. Preferably a scrimlayer made of thermoplastic fibrous material, thermo resistant to thetemperature range as given during the steam moulding is used.

A scrim is a thin nonwoven with a thickness between 0.1 and around 1(mm), preferably between 0.25 and 0.5 (mm). Preferably they have anincreased airflow resistance (AFR) of between 500 and 3000 (Nsm⁻³), morepreferably of between 1000 and 1500 (Nsm³).

The area weight of the scrim layer can be between 15 and 250 (g/m²),preferably between 50 and 150 (g/m²).

The scrims can be made from continuous or staple fibres or fibremixtures. The fibres can be made by meltblown or spunbond technologies.They can also be mixed with natural fibres. Preferably the materialchosen is heat stable over long time thermal load exposure. The scrimscan be made of fibres for example made of polyester, or polyamide, oroxidized, thermally stabilized polyacrylonitrile (PAN, also known asPANox) or a combination of fibres for instance of polyester andcellulose, or polyamide and polyester. The layer can be treated with theusual treatment necessary for the area of appliance, like for instanceoil repellent, water repellent, flammability treatment etc. A preferredexample of a scrim layer can be a nonwoven scrim layer made of polyesterand viscose fibres.

When the lining according to the invention is used in the passenger areaalso alternative covering layers, like nonwoven carpet or tufted carpetcan be used. These layers might be added also after the steam mouldingprocess step, by using conventional methods known in the art.

In the steam moulding process, a polyamide scrim layer can be used inaddition to laminate additional layers not directly adjacent to thereinforcement layer and/or to increase the amount of binding material inthe laminating zone. The polyamide can also be sprinkled in form ofpowder or flakes on the surface before adding additional layers, orapplied as a thin adhesive foil or netlike structure. So also otherlayers not directly adjacent to an reinforcement layer can be laminatedto the multilayer lining according to the invention for instancedifferent aesthetic covering layers, like for instance tufted ornonwoven carpet layer, flock material or nonwoven covering materials.

Multilayer Lining

The steam moulded multilayer lining produced according to the inventioncomprises a porous reinforcement layer, and at least a second layerchosen from a foam layer, a reflective layer, or a second porousreinforcement layer.

Additional layers can be used as well, such as additional foam layers orreinforcement layer or like aesthetic covering layers, or technicalscrim layers to further enhance the properties of the multilayer liningaccording to the invention. Also the use of similar layers withdifferent densities can be foreseen. If for instance two foam layers areused in direct contact, also the use of a polyamide binding layer, inthe form of a polyamide fibrous scrim, web, perforated foil, powder orflakes can be used. The use of polyamide as additional binding layer isadvantageous, as it will react to the steam in the same way as thematrix material in the reinforcement layer.

The porous reinforcement layer is mainly forming the structuralstiffness necessary. In most applications the lining is used as aself-supporting structure.

In a preferred application the multilayer lining comprises at least twolayers chosen from a porous reinforcement layer and an acoustical porousreinforcement layer. Preferably both layers are only connected to eachother at the rim of the lining or by using spacers, leaving a hollowspace in between the main surfaces of the layers. The hollow spacefunctions as an additional acoustic absorbing area and an acoustic andthermal decoupling zone. By using at least one acoustic porousreinforcement layer, the overall acoustic performance can be increased.

In the engine bay area different types of trim parts are used, forinstance engine encapsulation, engine top coverings as well as engineencapsulation that is mounted to the chassis of the vehicle. Furthermorealso other components like bonnet lining, outer bulkhead lining as wellas under engine shields and vertical elements along the front beams canbe placed in the engine compartment, to optimise the heat management ofthe engine compartment. In particularly a hood lining, firewall, orcover members adjacent the automotive engine like engine head cover,engine side panels, as well as other lining used in a vehicle inthermally exposed areas like the power train, including the gearbox,exhaust line, in particular heatshields mounted on body and power trainand/or the exhaust line. Also all types of under body panels used, inparticularly under the engine and the passenger compartment fall intothe scope of use for the inventive lining.

These and other characteristics of the invention will be clear from thefollowing description of preferential forms, given as non-restrictiveexamples with references to the attached drawings.

With help of the figures examples of adventurous combinations of layersfor specific applications will be given, to explain the invention evenfurther. However the invention should not be restricted to theseexamples, they are more meant to show the possibilities of the liningaccording to the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic overview of the steam treatment according to theinvention

FIG. 2 shows schematically the layering of the lining material accordingto the invention.

DESCRIPTION OF EMBODIMENTS

The production process will be explained in more detail using FIG. 1showing a steam mould comprising a lower mould half 2 and an upper mouldhalf 1. These two mould halves together define a mould cavity in whichthe semi-finished product will be at least consolidated. The mouldcavity can be formed in the wanted three-dimensional shape of the finaltrim part. As a semi-finished product a nonwoven fiber mat with a blendof binding material and reinforcement fibres 10 together with forexample foam layer 11. Preferably the two halves of the mould have inand out lets 7,8 through which the saturated steam can flow into themould cavity coming in direct contact with the multilayer material to beconsolidated and laminated. As saturated steam is used it is preferredthat the mould halves are kept warm to help pressure built up andprevent steam condensation. As steam condensation would cause a loss ofthe heat energy and would cause a soaking of the product with water. Inthe figure this is shown with the channels 3,4,5 and 6, showing a closedheating system for the mould halves. The heat of the mould halves is notimportant for the moulding of the lining.

The mould can have additional cutting and sealing elements 9 at itsedges; these can be moved and pushed independently, and they make aperimetral, pressure-tight sealing of the mould, i.e., through alabyrinth seal. After pressure-tight sealing of the mould, thesemi-finished product is exposed to saturated steam. The steam is usedas pressurised steam with a pressure in the mould cavity of betweenapproximately 2-20 (bar absolute), preferably a pressure of at least 9(bar absolute), and remains under this pressure in the mould cavityduring the entire consolidation period.

The process time is governed by steam pressure rising and release forconsolidation. Preferably before opening the press mould, thepressurised steam is released. Although some water does condensateduring the steam treatment and is left in the lining material accordingto the invention, this will dry up after opening of the mould, mainlydue to the residual thermal energy left in the core of the part.Surprisingly as soon as the steam pressure is taken away, the softeningand melting of the polyamide is reversed and the part is solidified. Thesteam process is therefore not only advantageous due to the short dwelltimes needed, it also eliminates any cool down time, needed with thetraditional compression moulding with dry systems before the mouldedpart can be removed from the mould cavity.

An example of a production method for a multilayer lining according tothe invention contains at least the steps of:

-   -   blending of 40 to 80% of reinforcement fibers and 20 to 60% of        polyamide matrix material in the form of fibers, flakes or        powder, and forming a web of said blend;    -   layering a first blended web and at least an additional layer        chosen from an open cell foam layer, a heat reflective layer, or        a second blended web of reinforcement fibers and polyamide        matrix material, inside a mould consisting of two mould halves;    -   treating the stacked multilayer material with pressurized        saturated steam, such that the polyamide matrix material in the        blended web is melting at a temperature under steam pressure        that is lower than the melting temperature of the polyamide        matrix according to DSC, thereby binding the reinforcement        fibers together thus consolidating the blended web forming a        porous reinforcement layer, and such that the stacked layers are        laminated together.

The mould halves can be fully closed at the start or can be closedduring the steam treatment, letting out some of the steam at thebeginning and/or at the end of the steam process. The saturated steampressure is preferably used in a range of 9 to 20 (bar absolute).

At least one additional scrim layer can be used to prevent the layeredmaterial from sticking to the mould. For instance a polyester-cellulosenonwoven scrim layer. The stacked multilayer material can contain evenfurther additional layers like an additional layer of a blended web, afoam layer. The polyamide matrix is preferably co-polyamide orpolyamide-6 or polyamide-6.6 or a mixture of these polyamides.

The moulded saturated porous multilayer lining, produced according tothe production process as disclosed can be directly moulded in a 3-Dshape to serve as an automotive trim part, like an engine bay coveringpanel, a top-, side- or undercover panel for an engine, an oil pancover, an under engine shield, a fire wall, an at least partiallycovering outer dash panel, an air guiding panel behind the cooler of theengine bay, a parcel shelf or a trunk load floor.

The steam moulded multilayer lining can be most advantageously used inareas of increase thermal load in a vehicle, like in close vicinity ofthe engine, power train and exhaust, but also in the trunk area or astrim part which are exposed to sunlight directly behind the window of acar, like parcel shelf or sunscreens,

FIG. 2 shows examples of possible multilayer lining materials. For thebasis of the lining according to the invention a porous reinforcementlayer or an acoustic porous reinforcement layer can be chosen. Thedifference is that the reinforcement layer is mainly made of polyamidematrix and reinforcement fibers. While the acoustic reinforcement layerconsists of the polyamide matrix and reinforcement fibers, however thereinforcement fibres is a blend of man made fibers and mineral fibers,for instance a blend of polyester and glass fibers, giving a more loftylayer after consolidation using the steam process.

FIG. 2 A shows an example with a porous reinforcement layer 10 and anopen cell foam layer 11, preferably an infrared reflecting layer 13 canat least partially cover at least one of the outer surfaces of thelining. While also a scrim layer 13 can be used to cover the outersurface of the lining. Instead of the porous reinforcement layer 10 anacoustic reinforcement layer can be used in situation where a higherlevel of sound absorption is needed.

Generally the reinforcement layers can replace injection-moulded plasticlayers, normally used in automotive trim parts as it has comparablestiffness properties. However due to its porosity it shows soundabsorbing properties, what is not the case for injection moulded parts.The use of additional absorbing layers even increases the soundabsorption.

For automotive trim parts used in a hot environment, particularly in theengine bay area, the combination of the porous reinforcement layer withan open cell foam layer is a good choice as it is very light and willsuit most acoustic requirements.

For trim part used in areas with an increased thermal load, like directengine mounted parts, the use of the combination of a porousreinforcement layer with the loftier acoustic porous reinforcement layeris a better option.

The heat reflective layer can be used in particularly at the surface orpartially at the surface that is directed to the heat source, and/orthat obtains the most direct heat energy.

The porous reinforcement layer 10 can also be combined with the acousticreinforcement layer 14 (FIG. 2B)

FIGS. 2C, and 2D show examples of at least three layers. In 2C a foamlayer 11 is sandwiched between two reinforcement layers 10, althoughhere the standard reinforcement layers are used also two acousticreinforcement layers or one of each type, can be used, depending on thesituation the multilayer lining is used. In particularly in high thermalload areas of the car where the foam needs thermal protection, this isan option. Preferably also with at least partially covering with areflective surface (not shown) and or a scrim layer.

FIG. 2 D shows a sandwich with a reinforcement layer 10 as a core layer,sandwiched between two foam layers 11. This layout is an advantage ifused in areas, where the passenger and or service personal come inregular contact with the surfaces. Glass fibers if they stick out of thelining surface have a nasty stinging effect, which is at the leastunpleasant. Foam would cover the glass fiber surfaces, preventing thissite effect. The reinforcement layer will bring the main structuralproperties, and therefore the foam can be a semi rigid or even a softeropen cell foam type as would have normally been used.

The invention claimed is:
 1. A production method for a multilayer liningfor thermal and sound insulation, comprising the steps of: blendingreinforcement fibers with a polyamide matrix material, in the form offibers, flakes or powder, to form a blended web; layering the blendedweb inside a mould with at least one additional layer forming a stackedmultilayer material, where each of the additional layers is an open cellfoam layer, a heat reflective layer, or a further blended web; treatingwith pressurized saturated steam the stacked multilayer material in themould, the pressurized saturated steam having a temperature sufficientto melt the polyamide matrix material in each blended web, the meltedpolyamide matrix material consolidating the reinforcement fibers in eachblended web into a porous reinforcement layer, while simultaneouslylaminating the layers of the stacked multilayer material into amultilayer lining.
 2. The method of claim 1, wherein the blended webcontains reinforcement fibers in the range of between 40 to 80% byweight, with the balance being the polyamide matrix material.
 3. Themethod of claim 1, wherein the saturated steam has a pressure in therange of 9 to 20 atmospheres absolute.
 4. The method of claim 1,wherein, in the layering step, at least one scrim layer is included inthe stacked multilayer material.
 5. The method of claim 1, wherein, whenpresent, the heat reflective layer only partially covers a layeradjacent thereto.
 6. The method of claim 1, wherein the reinforcementfibers are selected from a group comprising mineral based fibers, manmade fibers having a melting temperature higher than the meltingtemperature of the polyamide under steam pressure, and natural fibers.7. The method of claim 1, wherein the reinforcement fibers are a blendof mineral based fibers, and one selected from a group comprising manmade fibers having a melting temperature higher than the meltingtemperature of the polyamide under steam pressure, and natural fibers.8. The method of claim 1, whereby the reinforcement fibers forming thereinforcement layer is a mixture of 20-40% by weight of polyamidereinforcing fibers, 20-50% by weight of glass fibers, and 20-50% byweight of polyester and/or natural fibers.
 9. The method of claim 1,wherein the polyamide matrix is polyamide-6 or polyamide-6,6 orco-polyamide or a mixture of different types of polyamide.
 10. Themethod of claim 1, wherein the open cell foam layer, when present, is askinless foam.
 11. The method of claim 10, wherein the open cell foamlayer is polyurethane (PUR) foam or polyester (PET) foam or a fiberfilled foam.
 12. The method of claim 1, wherein, in the treating step,the mould conforms the multilayer lining into a three dimensional shape.13. The method of claim 1, wherein the treating step comprises thesubsteps of: closing and clamping the mould with the stacked multilayermaterial layered therein: applying the pressurized saturated steam intothe closed and clamped mould, melting the polyamide matrix material;releasing the steam pressure from the closed and clamped mould,resolidifying the polyamide matrix material; and unclamping and openingthe mould to release the multilayer liner as a stiff part.
 14. Themethod of claim 1, wherein the pressurized saturated steam has asaturation temperature that is between the temperature at which thepolyamide matrix material melts in the presence of pressurized saturatedsteam and the temperature at which the polyamide matrix material meltsaccording to Differential Scanning calorimetry.